The ship-builders of the Mediterranean ports retained the type of the classical galley, depending mainly upon oars for its propulsion. The hull was much longer than in the northern type of sailing ships and did not rise far above the water; both characteristics depended on the need of placing the oarsmen where they could work to advantage. The three square sails were a comparatively late improvement on the earlier rig, which consisted ordinarily of one sail; a fair wind was utilized for helping the boat on its course, but the chief reliance was placed on the oars. =80. Backwardness of the art of navigation.=—The control of a ship is as important as its construction, if it is to serve commerce, and the growth of maritime commerce in the last centuries of the Middle Ages was due as much to improvements in the art of navigation as to superior ship building. During the early Middle Ages, as in ancient times, ship captains took their lives in their hands when they ventured out of sight of a familiar coast. The only means they had for determining their position at sea was “dead-reckoning,” _i.e._, estimating the distance that they had traveled from a known point, and the course that they had steered; and to know their course they had to rely upon the stars, which of course were obscured in stormy weather, when their help was most wanted. It was customary, on voyages in the open sea, to sail due north or south to the parallel of the destination, then to turn at right angles and sail due east or west; errors in the course of 8 or even 10 degrees were not uncommon. The means of fixing the course in any weather, the mariner’s compass, which was discovered by the Chinese, and is supposed to have been known to the Arabs at this time, was still unknown in Europe.